R-process Element Cosmic Rays from Neutron Star Mergers

Neutron star mergers (NSMs) are one of the most plausible sources of r-process elements in the universe. Therefore NSMs can also be a major source of ultra-heavy elements in cosmic rays. In this paper, we first estimate the contribution of r-process elements synthesized in NSMs to the ultra-heavy element cosmic rays (UHCRs) by calculating transport equations that take into account energy loss processes and spallations. We show that the flux of UHCRs accelerated by NSMs themselves fluctuates by many orders of magnitude on the timescale of several million years and can overwhelm UHCRs accelerated by supernova remnants (SNRs) after an NSM takes place within a few kilo-parsec from the solar system. Experiments with very long exposure times using meteorites as UHCR detectors can detect this fluctuation. As a consequence, we show that if NSMs are the primary source of UHCRs, future experiments using meteorites have a possibility to reveal the event history of NSMs in the solar vicinity. We also describe a possible difference in the abundance pattern and energy spectrum of UHCRs between NSM and SNR accelerations.